spray bar location?

On many of the conversions of R/C engines the NVA/spray bar is put in through the holes where the R/C carb set screws were that held the darb in place. On one of my engines the disatance above the engine centerline is less than 1/2 inch. I suspect that usually you would mount the engine on some form of spacers to get the NVA/spray bar more than 1/2 inch from the engine mounts to allow room for a 1 inch high fuel tank (and room for tank adjustment) . On some planes this will change the thrust line and require mods to the nose shape... Is there any problem with drilling the the venturi insert and mounting the NVA/spray bar above the engine casting?

>On many of the conversions of R/C engines the NVA/spray bar
>is put in through the holes where the R/C carb set screws
>were that held the darb in place. On one of my engines the
>disatance above the engine centerline is less than 1/2 inch.
>I suspect that usually you would mount the engine on some
>form of spacers to get the NVA/spray bar more than 1/2 inch
>from the engine mounts to allow room for a 1 inch high fuel
>tank (and room for tank adjustment) . On some planes this
>will change the thrust line and require mods to the nose
>shape... Is there any problem with drilling the the venturi
>insert and mounting the NVA/spray bar above the engine
>casting?

Some of the manufacturer's conversions of RC type engines do this. However, moving the needle that far away from the shaft can have other effects and I don't recommend it. And, surprisingly, this does not always affect the height of the tank. There are other factors here which I still have not understood that will determine the final location of the tank. Al Rabe did an experiment once with an adjustable needle height on one of his engines and reported no difference in tank location. I don't know. We have a Fox 35 engine that has been modified with a Fox 35 piston (same insides otherwise, including cylinder and porting).

The stock 35 in that engine works with the tank in one locatin and the modifiec engine requires the tank to be raised a full 1/8 inch. The Thunder Tiger 42 engine is an outside clone of the FP 35/40 (although the "innards" are totally different). Because of the design of the case, I end up drilling the needle slightly lower than the "normal" half inch above the thrust line. It doesn't affect the location of the tank at all.

So, what I am suggesting is, go with what you have. Mount the needle where it fits with the holes that are there and you will probably find that it will work just fine.

I had the same question in my mind some time back and ended up making a venturi insert with the NVA above the the set screw holes in the intake casting. My justification is; I was putting the NVA at the same height as the R/C carburator NVA. For the record, I was converting a Series 4011 K&B .40 R/C to C/L. I made a engine test stand from a hard wood board, mounted the engine and mounted the tank to the board. I did not experiment with tank height. The engine ran fine and consumed 1 oz. of fuel (2 cycle running) in 90 seconds. I then took a another K&B .40 with the R/C carburator installed and ran it the same way. It also used the same amount of fuel in about the same amount of time. If anyone want pictures of the installation, send me a reply via this posting.
Vern Sundstrom:)

I've done it both ways with with K&B 4011's and Tower 40's. Works fine either way. However, my experience is that the uniflow outlet in the fuel tank needs to be pretty close to the vertical position of the spraybar hole.

I am curious about the K&B 4011, Will it make a decent stunt engine without mods? Most likely will run a stong 2 stoke type run. Shimming the tank or raising the engine seems to be easier than drilling and venturi mods. Just do it when you build the plane. The best is to be able to move the tank around that way the nose spinner will stay in the same place, don't ask me how I know this. Jim J

>I've done it both ways with with K&B 4011's and Tower 40's.
>Works fine either way. However, my experience is that the
>uniflow outlet in the fuel tank needs to be pretty close to
>the vertical position of the spraybar hole.
>
>Jim

Ron B.
F4Fguy

Got it in one!!!

Hello, one of you gentleman asked for a picture last week of my K&B .40 venturi/NVA set-up. Please send me your email and I'll send back a picture of the set-up. Vern Sundstrom

I ran stock K&B 4011's, except for a CL venturi, for several years with great happiness. I am now fooling with them again. My old setup is unsatisfactory and I am trying various things to make them work to suit me.

Jim, that's interesting as I have one I was going to pass on but it is new and I always liked this engine. It was a work horse and not a speed demon, if you know what I mean. I had one in a Quickee 500 RC plane and was quick to notice the difference between it and the Max H 40 I was also running at the time in a New Era 40. Years ago I know there was some experimenting going on with the K&B 40 used by Stan Powell and Les McDonald. The ST 46 took over and every one moved on. This engine weighs a bit more but I believe it to have a bit more umph than the Modified FP 40 and quite possibly the LA 40, I would put it in a Humungous, with it's thick airfoil the OS engines are a bit challenged to fly this plane right unless there is no wind. The Humungous has become a great test bed for new engines. My plane came in at 43 oz and seemed a bit on the light side if there is such a thing. What size venturi do you think is a good place to start? .280? Jim J.

I flew my Humongous with a K&B 4011 with great satisfaction. I flew it for several years; made the top 20 in OTS at the VSC with it (17th, I think). I ran an APC 11 X 5, a very small venturi (a 290 with a piece of al tubing in it. 64 ft lines. Muffler pressure and uniflow, Sig Champion 10%, 20% oil 50/50. Fox 2 volt plug.

This sounds great, now I can the two oz of lead out of the nose and still use the .015s I made up for the plane. I used to put a piece of cork in the venturi when I was growing up....still wondering where I got that idea. The old square intake venturi Enyas would usally be found with the #3 venturi and we would block off half of it and get great runs. I guess something like .265 would be OK. I have wanted to make one on my drill press, now I have a chance. Thanks Jim